Basal crevasses in Larsen C Ice Shelf and implications for their global abundance

摘要

Basal crevasses extend upwards from the base of ice bodies and can penetratemore than halfway through the ice column under conditions found commonly onice shelves. As a result, they may locally modify the exchange of mass andenergy between ice shelf and ocean, and by altering the shelf's mechanicalproperties could play a fundamental role in ice shelf stability. Althoughearly studies revealed that such features may be abundant on Antarctic iceshelves, their geometrical properties and spatial distribution has gainedlittle attention. We investigate basal crevasses in Larsen C Ice Shelf usingfield radar survey, remote sensing and numerical modelling. We demonstratethat a group of features visible in MODIS imagery are the surfaceexpressions of basal crevasses in the form of surface troughs, and find thatbasal crevasses can be generated as a result of stresses well downstream ofthe grounding line. We show that linear elastic fracture mechanics modellingis a good predictor of basal crevasse penetration height where stresses arepredominantly tensile, and that measured surface trough depth does notalways reflect this height, probably because of snow accumulation in thetrough, marine ice accretion in the crevasse, or stress bridging from thesurrounding ice. We conclude that all features visible in MODIS imagery ofice shelves and previously labelled simply as "crevasses", where they arenot full thickness rifts, must be basal crevasse troughs, highlighting afundamental structural property of many ice shelves that may have beenpreviously overlooked.